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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
408 PM CDT Sat Aug 29 2015

Short term...(this evening through sunday)
issued at 311 PM CDT Sat Aug 29 2015

As if the shorter days were not enough to show you the sun is
getting weaker as we end August...the stubbornness of the stratus
this morning should be all the proof you need that the seasons are
about to change. Add in a lack of winds and mechanical mixing and
it will take until almost 21z to finally clear the stratus out.
These light winds and weaker mixing have even impacted western Minnesota
where the sun has been out all day...but temperatures have struggled to
warm out of the 70s.

For tonight...expect stratus to expand for the third night in a row
to the west of the remnant surface trough that extends from Missouri up
toward western lower mich. Two nights ago we saw this stratus over north
central Minnesota...last night it was across Iowa up into southern Minnesota into central
WI. Tonight...the stratus will form a little farther southeast of
its previous nights location...so that will put less of the area
under the gun for seeing low stratus again. Based on sref probs for
ceilings less than 3k feet...expect threat for stratus tonight to be
greatest from along...south and east of a line from Fairmont...to
the Twin Cities and Ladysmith. Not helping the fog/stratus tonight
is the fact that we will be picking up a pressure gradient...with
more persistent south winds expected through the night...which will
help keep mixing a little better. Beside lowering the stratus threat
some...mixing from these strong winds will make any stratus we do
see tomorrow morning easier to break up than we saw today.

For Sunday...did nudge highs down a couple of degrees...mainly in
western Minnesota. 925-850 temperatures came down a nudge from what models were
showing last night. Where 90s are in the Dakotas today is
associated with 925-850 temperatures of 28c in the NAM/GFS and 26c in
the European model (ecmwf) /the NCEP models have had a warm bias all Summer/.
Tomorrow...those isotherms stay west/northwest of the mpx area...so mixed
in some bias corrected European model (ecmwf) numbers to the going forecast. This
cooled the west a couple of degrees while keeping eastern parts of the
mpx County Warning Area more or less unchanged.

Long term...(sunday night through saturday)
issued at 311 PM CDT Sat Aug 29 2015

By Sunday night...the upper ridge will be in place across our
area...extending from the southwestern U.S. Into the upper
Midwest on the 500mb height level...with 588 dm heights pushing
into southwestern Minnesota. Any semblance of a jet stream will be north
of the Canadian border through Tuesday. 850mb temperatures around 20c
both Monday and Tuesday with low level southwesterly flow spell
day time highs in the middle to upper 80s.

On Wednesday...a highly amplified trough will come onshore in the
Pacific northwest and will be the feature to keep an eye on as we
head toward Labor Day weekend. With this pattern...a mostly dry
pattern for our area through the work week...with occasional
chances of very sporadic showery and isolated thunder activity.
With the low level heat though...we will likely be capped for
several days...and even with a weak shortwave rippling through middle
week...the forcing associated with said wave may be too weak to
overcome the cap. The probability of precipitation in the current forecast include broad
slight chance probabilities...which is likely too high an
widespread given the capped environment...but at this range we
cant get too precise with the location of the best chance for a
few showers or storms to get going.

&&

Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 105 PM CDT Sat Aug 29 2015

Combination of the ever weakening late August sun and a lack of
mechanical mixing with the light winds has resulted in the stratus
being stubborn this morning. However...it is now rapidly mixing
out and it will be a thing of the past by 19z. No weather issues
are then expected until tonight...when we will likely see a repeat
of the stratus expansion. Thursday night this stratus area was in
north central Minnesota...last night it moved to over the mpx area...and
based on sref probs for ceilings under 3k feet...this stratus area will
setup a bit farther southeast tonight. This will mean more of the
mpx terminals will stay out of the low conditions tonight...with
most likely locations for stratus returning being rnh/eau. For
Sun morning...we will have a stronger pressure gradient and
therefore more surface winds...so any stratus we do see Sun morning
should mix out quicker than it did today.

Kmsp...we will quickly go VFR and remain as such through much of
tonight. Fully expect another round of stratus to develop...but
looks to be farther southeast than it was this morning. At the
moment...think msp stays clear of the stratus...especially
considering we will keep a light south wind tonight. Still may be
close so added a few003 to the cloud group at 11z to hint at that
possibility again.

/Outlook for kmsp/

Mon-Wed...VFR. Winds S 5-15kt



&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$

Short term...mpg
long term...speed
aviation...mpg

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